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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchThe “RPC server is unavailable” message, often shown with error code 0x800706BA, means a Windows client could not complete a Remote Procedure Call to another service or computer. The usual fault is not the RPC service itself but a failure to reach the dynamically assigned port after the initial connection to TCP port 135. Work through name resolution, required services, port 135, dynamic-port filtering and—only when necessary—an administrator-controlled port range.
What the RPC error means
Remote Procedure Call (RPC) allows a Windows program to ask a service on the same computer or another computer to perform an operation. Domain logon, Windows Management Instrumentation (WMI), Microsoft Management Console (MMC) snap-ins, file and printer administration, and Active Directory replication can all depend on RPC.
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RPC normally uses two connections. The client first contacts the RPC Endpoint Mapper on TCP port 135. The mapper identifies the service and returns a dynamically allocated endpoint. The client then opens a second connection to that dynamic port. A firewall or security device must permit both connections. Microsoft describes the most common failure as the client being unable to connect to the dynamic port that was allocated.
The wording does not prove that a remote computer is powered off, that Windows is damaged, or that malware is present. It identifies a communication failure somewhere between the requesting program and the target service.
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Identify the failing stage before changing settings
Use the scope, workload and network stage to decide where to investigate. This prevents opening unrelated ports or changing services that are not involved.
| What you observe | Likely stage | First check |
|---|---|---|
| Only a computer name fails; its IP works | Name resolution or DNS | Resolve the name and compare it with the target IP |
| Port 135 cannot be reached | Target offline, routing, VPN or firewall before the mapper | Connectivity and TCP 135 |
| Port 135 reports listening, but WMI, MMC or logon still fails | Dynamic RPC port blocked | Host and network firewalls, VPNs and security appliances |
| One service fails on one host | Target service or host firewall | Service state and local firewall on that host |
| Many hosts or an entire subnet fail | DNS, routing, network firewall or policy | Compare a working and failing host, then inspect shared controls |
| Active Directory replication reports 1722 | DNS or required RPC ports filtered | DNS records and firewall rules between domain controllers |
Step 1: Confirm the target computer and name resolution
- Verify that the target PC or server is powered on, connected to the expected network and not disconnected from a required VPN.
- From the Windows 10 client, test the target by its computer name. Then test the same target by IP address where that is appropriate for your network. A name that resolves to the wrong address is a DNS problem, not a reason to open more firewall ports.
- Use a name-resolution check such as
nslookup TargetNameand compare the returned address with the target’s current address. Correct stale, duplicate or incorrectly scoped DNS records before continuing. - If the name and IP both fail, check routing, VLAN or VPN access and host availability. If the IP works but the name fails, fix DNS or the local resolver configuration first.
Incorrect DNS settings are specifically associated with domain-logon RPC failures. Changing the firewall while the client is contacting the wrong address can hide the real fault and create unnecessary exposure.
Step 2: Verify Windows services
Core RPC service
- Press
Win+R, enterservices.msc, and press Enter. - Locate Remote Procedure Call (RPC). Its status should be Running, and its startup configuration must not be Disabled.
- If it is stopped and Windows permits you to start it, start the service and retry the operation. If it cannot be started, record the exact message and investigate dependencies or system policy rather than repeatedly forcing it.
Do not disable RPC to “test” the error. Many Windows components rely on it, so disabling the service can create additional failures.
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Additional services for domain logon
For a domain-logon failure, also check TCP/IP NetBIOS Helper and Remote Registry in services.msc. Microsoft’s domain-logon guidance calls for these services to be verified and configured for automatic startup where required by the environment. Apply the organization’s security policy when enabling Remote Registry; do not enable services broadly on systems that do not need them.
Step 3: Test the RPC Endpoint Mapper on TCP 135
Port 135 is only the first stage, but testing it separates a basic reachability problem from a dynamic-port problem. Microsoft’s PortQry procedure can show whether the mapper is listening and which endpoint it returns.
- Open Command Prompt as an administrator on the Windows 10 client.
- Run
Portqry.exe -n <ServerIP> -e 135, replacing<ServerIP>with the target’s address. - Read the result. A successful test resolves the address, reports
TCP port 135 (epmap service): LISTENING, and displays the dynamic port returned by the endpoint mapper.
If PortQry cannot connect, inspect the target’s power and network state, routing, VPN path and every firewall between client and server. A non-listening result can also mean the target is not offering the expected service, so confirm the workload and service on the destination.
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Step 4: Check the dynamic RPC connection
A listening mapper does not prove that the application can work. The client must open a second TCP connection to the dynamic endpoint returned by port 135. Microsoft identifies blocked dynamic ports, middle devices and destination filtering as common causes.
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- On the target, review the Windows Defender Firewall rules that apply to the failing workload, such as WMI, remote administration or the relevant application. Confirm that inbound RPC traffic is allowed for the correct network profile and scope.
- Review outbound rules on the client if your organization uses restrictive egress filtering.
- Check network firewalls, VPN concentrators, routers and security appliances for rules that permit TCP 135 but deny the returned dynamic port. A rule that allows only 135 is incomplete for ordinary RPC.
- Check the destination server’s firewall and any endpoint-security policy. Filtering at the destination can look identical to filtering in the middle of the path.
- Retry the original operation after each controlled change. Test from the same client and network segment so that you know which change affected the result.
Do not open every port on every profile as a quick fix. Limit rules to the required hosts, subnets, protocols and network profile, and document temporary exceptions so they can be removed.
Step 5: Use a constrained RPC range only when your design requires it
Some organizations cannot pass the default dynamic RPC behavior through their firewalls. An administrator can configure a defined RPC port or range, then permit exactly that range between the required systems. This is an infrastructure change, not a normal workstation tweak.
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- Confirm that the firewall architecture truly requires constrained ports and identify which RPC-dependent services must be supported.
- Choose a documented port or range that matches the organization’s security design and avoids conflicts with other applications.
- Configure the RPC-dependent service and every relevant firewall consistently. A range configured on only one side will still produce the unavailable-server error.
- Test port 135 and then the assigned constrained endpoint from an approved client.
- Record the change, ownership and rollback procedure. Revisit the rule when servers, network zones or security policies change.
Do not invent a range from an internet example. The correct values depend on the service, Windows configuration and the organization’s network controls.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Domain logon, WMI, MMC and Active Directory-specific checks
Domain logon
When the error appears while signing in to a domain, verify DNS first, then check time and time-zone settings on the client and domain controllers. Also verify TCP/IP NetBIOS Helper and Remote Registry as described earlier. A clock or time-zone mismatch can prevent authentication even after RPC connectivity is restored.
WMI and MMC
WMI queries and many MMC remote snap-ins use RPC. Apply the same sequence: resolve the host name, confirm services, test TCP 135, identify the dynamic endpoint and inspect host, network and destination filtering. If one snap-in fails while another works, compare the service and firewall rules for that workload instead of assuming all RPC is broken.
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Active Directory replication error 1722
For replication error 1722, verify that domain controllers resolve one another through correct DNS records and that required ports are not blocked by a firewall or third-party application. Test in both directions where replication is bidirectional; one-way reachability can leave replication failing on only one partner.
Step 6: Capture a network trace when the checks do not isolate the fault
When name resolution, services, port 135 and firewall reviews do not reveal the break, collect evidence instead of making broader changes. On the client, open an elevated Command Prompt and run:
netsh trace start scenario=netconnection capture=yes tracefile=c:client_nettrace.etl maxsize=512 overwrite=yes report=yes
Reproduce the RPC failure once, then stop the trace with:
netsh trace stop
Where possible, collect a corresponding trace on the server. Inspect whether the client receives the dynamic port from the endpoint mapper and whether packets to that port are retransmitted or rejected. A trace showing a successful TCP 135 exchange followed by retransmissions to the allocated endpoint points toward dynamic-port filtering or a destination-side problem. Preserve timestamps, source and destination addresses, VPN state and the exact operation that failed when escalating to your network or Windows administrator.
Quick Recap
Recovery checks after a change
- Repeat the original operation, not just the port test. A listening endpoint can exist while the application service is stopped or denied by policy.
- Test from a second authorized client when the scope is unclear. If only one client fails, compare its DNS, VPN, firewall profile and local policy with a working client.
- Test a second authorized target when an entire subnet appears affected. This helps distinguish a single server fault from a shared network control.
- Remove temporary firewall exceptions and restore the prior policy after the cause is confirmed.
- For domain environments, check that time, DNS and replication remain healthy after the RPC fix; restoring one connection should not be mistaken for repairing every domain dependency.
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